What is the differential diagnosis and appropriate workup for a 36-year-old male presenting with cough, body aches, headache, tachycardia, mild tachypnea, and chest discomfort, with a history of a recent fall and complex regional pain syndrome (CRPS), and vital signs showing hypertension, tachycardia, and mild hypoxemia?

Differential Diagnosis and Workup for 36-Year-Old Male with Respiratory Symptoms, Tachycardia, and Recent Head Trauma

This patient requires immediate evaluation for pulmonary embolism (PE) given recent travel, immobility from complex regional pain syndrome, tachycardia (126 bpm), tachypnea (24/min), chest discomfort, and recent fall—all representing significant risk factors for venous thromboembolism that supersede the viral symptom presentation. 1

Priority Differential Diagnoses

Life-Threatening Conditions (Must Rule Out First)

Pulmonary Embolism (PE) - This is the most critical diagnosis to exclude given:

• Recent travel within 8 weeks (major risk factor) 1
• Immobility from chronic regional pain syndrome in left leg 1
• Tachycardia (126 bpm) and tachypnea (24 respirations) are classic PE findings 1
• Chest discomfort is present 1
• The combination of these factors places him at intermediate-to-high clinical probability for PE 1

Acute Coronary Syndrome/Type 2 Myocardial Infarction - Must consider because:

• Tachycardia and chest discomfort in the setting of supply-demand mismatch 1
• Viral illness can precipitate Type 2 MI through increased metabolic demand 1
• Hypertension (163/76) increases cardiac afterload 1

Delayed Traumatic Intracranial Hemorrhage - Critical given:

• Fall with head impact 2 weeks ago, never evaluated 2
• Nausea/vomiting the day after fall (classic post-concussive symptoms) 2
• Current headache may represent evolving subdural hematoma 2
• Acute spontaneous subdural hematomas can present in middle-aged adults without obvious ongoing trauma 2

Secondary Differential Considerations

Community-Acquired Pneumonia - Possible but less likely primary diagnosis:

• Cough, body aches, fever (98°F is actually normal, not febrile) 1, 3
• However, normal oxygen saturation (96% on room air) argues against significant pneumonia 1, 4
• Tachycardia and tachypnea are disproportionate to the mild symptoms 4

Pneumonia with Concealed PE - Important consideration:

• Pneumonia can mask PE, particularly when systemic symptoms predominate 5
• Patients may initially improve with antibiotics but then worsen if underlying PE is present 5

PVL-Positive Staphylococcus Aureus Pneumonia - Less likely but potentially catastrophic:

• Can present with rapid deterioration and septic shock 1
• However, patient lacks fever and severe hypoxemia typical of this entity 1

Immediate Workup and Interventions

Critical First Steps

Electrocardiogram (ECG) - Obtain immediately:

• Evaluate for ST-segment changes suggesting acute coronary syndrome 6
• Look for signs of right heart strain (S1Q3T3 pattern, right axis deviation, T-wave inversions in V1-V3) suggesting PE 1
• Tachycardia itself warrants ECG evaluation 6

Cardiac Troponin - Draw immediately:

• Essential to evaluate for Type 1 or Type 2 myocardial infarction 1
• Elevated troponin in setting of tachycardia and chest discomfort requires urgent cardiology evaluation 1, 6

D-Dimer - Critical for PE evaluation:

• Given intermediate-to-high clinical probability for PE, proceed directly to imaging rather than relying on D-dimer alone 1
• However, obtain D-dimer as it provides additional risk stratification 1

Imaging Studies (In Order of Priority)

CT Pulmonary Angiography (CTPA) - Most urgent imaging study:

• This is the definitive test for PE in hemodynamically stable patients 1
• Should be performed emergently given high clinical probability 1
• Do not delay for D-dimer results in this intermediate-to-high probability patient 1

Non-Contrast Head CT - Obtain urgently (can be done simultaneously with CTPA):

• Mandatory given fall 2 weeks ago with head impact and ongoing headache 2
• Acute spontaneous subdural hematomas can present in middle-aged adults 2
• Post-traumatic nausea/vomiting followed by persistent headache is concerning 2

Chest X-Ray - Obtain but recognize limitations:

• Helps evaluate for pneumonia but normal chest X-ray does not exclude PE 1, 4
• May show infiltrates if pneumonia present 1, 3
• Less sensitive than CT for pulmonary pathology 4

Lower Extremity Venous Duplex Ultrasound - Consider if CTPA delayed:

• Finding DVT in patient with suspected PE is sufficient to initiate anticoagulation 1
• Chronic regional pain syndrome in left leg may predispose to DVT 1

Laboratory Studies

Complete Blood Count with Differential:

• Evaluate for leukocytosis (pneumonia, infection) or lymphopenia (viral illness) 1
• Assess hemoglobin and platelets before anticoagulation 1

Comprehensive Metabolic Panel:

• Assess renal function before contrast administration for CTPA 1
• Evaluate for metabolic derangements 1

Arterial Blood Gas (if hypoxemia worsens):

• Current oxygen saturation 96% on room air is borderline 1
• ABG provides precise PaO2 and helps calculate A-a gradient 1, 7

Procalcitonin and Blood Cultures:

• If pneumonia suspected, obtain before antibiotics 1
• Procalcitonin helps differentiate bacterial from viral infection 1

Brain Natriuretic Peptide (BNP):

• Helps differentiate cardiac causes of dyspnea 6
• Elevated in right heart strain from PE 1

Bedside Echocardiography

Transthoracic Echocardiography - Perform if available:

• Evaluate for right ventricular dysfunction suggesting PE 1
• Assess for regional wall motion abnormalities suggesting ACS 6
• In hemodynamically stable patients, absence of RV dysfunction does not exclude PE but helps risk stratify 1

Immediate Management Pending Workup

Do NOT initiate anticoagulation until head CT excludes intracranial hemorrhage given recent head trauma 2

Supplemental Oxygen - Maintain SpO2 >94% 1

Continuous Cardiac Monitoring - Given tachycardia and chest discomfort 6

Intravenous Access - Establish for potential contrast administration and medications 1

Critical Clinical Pitfalls

The "viral syndrome" presentation may be a red herring - The disproportionate tachycardia (126 bpm) and tachypnea (24/min) with only mild hypoxemia (96% SpO2) and normal temperature (98°F) suggests a more serious underlying process than simple viral illness 1, 4

Recent travel is a major PE risk factor - Travel within 8 weeks significantly increases PE risk, and this must be prioritized over the cough symptoms 1

Head trauma cannot be ignored - A fall with head impact 2 weeks ago followed by nausea/vomiting and persistent headache requires urgent neuroimaging before any anticoagulation 2

Pneumonia and PE frequently coexist - If pneumonia is confirmed, maintain high suspicion for concurrent PE, especially if clinical improvement plateaus or reverses with antibiotic therapy 5

Hypertension (163/76) in this context is concerning - This may represent pain, anxiety, or increased sympathetic tone from PE or other serious pathology 1, 6